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From: Niklas Holsti <niklas.holsti@tidorum.invalid>
Newsgroups: comp.lang.ada
Subject: Re: How to get Ada to ?cross the chasm??
Date: Wed, 9 May 2018 00:28:53 +0300
Organization: Tidorum Ltd
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Xref: reader02.eternal-september.org comp.lang.ada:52132
Date: 2018-05-09T00:28:53+03:00
List-Id: <comp.lang.ada>

On 18-05-07 10:25 , Dmitry A. Kazakov wrote:
> On 07/05/2018 03:31, Paul Rubin wrote:
>> "Dmitry A. Kazakov" <mailbox@dmitry-kazakov.de> writes:
>>> This is easily done in present Ada using handles to a
>>> reference-counted objects.
>>
>> That's not much different from gc from the user's perspective, other
>> than problems handling cycles.
>
> Cycles are easily avoidable too by separating target objects and
> handles. All target objects types go into the private part of the
> package. When only handles are visible there is no way the end user
> could construct a cycle.

True for a single such data structure; much harder if the client 
combines different, independently implemented data structures and 
stores, in one structure, handles that point at the other structure, and 
perhaps in the other direction too. Since the implementations of the two 
data structures are ignorant of each other's existence, neither can 
detect such cross-structure cycles, I believe.

GC-based languages handle such cross-structure cycles in the same way as 
within-structure cycles.

-- 
Niklas Holsti
Tidorum Ltd
niklas holsti tidorum fi
       .      @       .